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1. Field of the Invention
This invention relates generally to reinforcement of walls, especially masonry walls of solid, unitary cast concrete construction or block walls. This invention also relates to reinforcement of walls constructed of wood, metal or other materials. More specifically, the invention relates to reinforcement of a wall by adhering fiber-reinforced polymer composite (FRPC) material to at least one surface of the wall.
2. Description of the Related Art
The earth adjacent a subterranean wall exerts a vertical force resulting from its weight, and it exerts a substantial horizontal force, due to its fluid properties, that increases in proportion to depth. Although this horizontal force is otherwise opposed and counteracted by the adjacent soil in other places within the earth, the wall, which is interposed within the earth, must support that lateral load.
Any subterranean wall may at some subsequent time be found structurally inadequate to satisfactorily resist the horizontal force of the earth directed against the exterior surface of the wall W. There are many diverse factors that can cause a wall to become structurally inadequate to resist the forces exerted against its exterior surface, thus requiring some remedial action to prevent or lessen the likelihood of serious damage or possibly catastrophic failure.
Reinforcing of concrete masonry structures by means of exterior application of rigid metal plates to surfaces of such structures by mechanical fastening devices is a known practice. An example of this practice is illustrated in U.S. Pat. No. 5,640,825 issued Jun. 24, 1997 to Ehsani, Mohammad R., et al. These plates are utilized to subsequently attach the ends of elongated, flexible straps of sheet-form having short, randomly oriented non-metallic fibers with the straps secured in a horizontally disposed position to the wall""s surface by an adhesive epoxy that is then cured. The metal plates engage with longitudinal end portions of the straps and are mechanically secured to adjacent structure that supports the wall.
It is also known to strengthen load-bearing concrete floors by using carbon fibre reinforced polymer (CFRP) strips. This is accomplished through bonding of elongated strips of CFRP to the underside of horizontally disposed concrete floors with these strips counteracting tensile forces. These CFRP strips may also be utilized for strengthening roof sections to better accommodate roof loading generated by wind, accumulations of snow and combinations of wind and snow. The CFRP strips are applied in laterally spaced parallel relationship by use of a suitable adhesive. These strips may also be applied in overlying relationship to a previously applied set but not to the surface of the concrete structure being strengthened. These strips are disposed in orthogonal arrangement to the previous set and adhesively bonded thereto.
Three previously issued U.S. patents disclosing related subject matter were noted as a result of investigating existing reinforcing techniques utilized in strengthening concrete structures. These patents are listed as follows:
[1] U.S. Pat. No. 5,308,430 issued May 3, 1994 to Saito, Makoto, et al.;
[2] U.S. Pat. No. 5,326,630 issued Jul. 5, 1994 to Saito, Makoto, et al.; and
[3] U.S. Pat. No. 5,447,593 issued Sep. 5, 1995 to Tanaka, Tuneo, et al.
Each of these three patents discloses a similar structural unit that provides the tensile stress resistive component for effecting strengthening of the concrete structural element to which it is applied. Each comprises a plurality of elongated fibers aligned in parallel groups embedded in an uncured matrix of thermosetting resin in a sheet structure. This structural sheet is adhered with a thermosetting resin applied to a surface of the structural element to be strengthened. The sheets are positioned on the structural element to obtain the most effective utilization of the tensile attributes of the fibers. Along with positioning of the fiber sheets with the resin, the entire mass is subjected to ambient room temperature or application of heat at an elevated temperature appropriate to cure the matrix and resins.
Another technique previously used in effecting strengthening of walls comprises utilization of a plurality of elongated structural steel beams vertically disposed in spaced parallel relationship along the inwardly facing surface of a wall. These beams are of a size and cross-sectional configuration to have sufficient strength to counteract inward flexing of the wall that would otherwise result from any unexpected excessive increase in horizontally directed forces applied to the outwardly facing surface of the wall. Each of the beams, which may be of xe2x80x9cIxe2x80x9d, xe2x80x9cTxe2x80x9d, xe2x80x9cLxe2x80x9d-shaped angle, xe2x80x9cCxe2x80x9d-shaped channel or other suitable configuration, has a flat-surfaced component that is positioned in contacting engagement with the wall""s surface. The upper end of each beam is mechanically secured to an overlying joist and the bottom ends are fixed to the floor, which, in a basement wall-strengthening situation, is typically formed of concrete. A typical technique of securing a beam to a concrete floor comprises forming a socket in the floor for each beam, inserting the beam""s lower end in a respective socket, filling the socket with concrete which is permitted to harden thereby holding the beam upright and against the wall, and then securing the upper end to a joist. This technique results in a structure that is not only objectionably intrusive into a basement""s interior space but is a costly and time-consuming procedure.
A major aspect of this invention is a method of strengthening vertically disposed masonry walls to increase their ability to resist laterally directed forces that may be applied to one surface of the wall. Once practiced, the method enhances the lateral strength of basement walls of residential homes and similar walls of commercial buildings. These walls are generally substantially subterranean with earth surrounding the building and disposed against the exterior surface of the wall.
A basic embodiment of this invention comprises a rigid, elongated, fiber reinforced polymer plate that is adhesively bonded to an interior surface of a masonry wall to strengthen the wall to resist horizontally directed forces applied to its exterior surface. The plate is relatively thin compared to its width and is positioned in a generally vertical orientation with one of its major, flat surfaces placed in coplanar relationship to the wall""s surface to which it is bonded by an intervening layer of an adhesive bonding agent. The plate is preferably of a length to extend the full height of the wall.
For a wall of substantial length a plurality of plates are used with the plates being disposed in spaced parallel relationship along the length of the wall. Spacing of the plates and the number required for a given length of wall is dependent upon the maximum expected earth and water loading forces to be applied horizontally against the exterior surface of the wall. Other factors entering into this determination are the thickness and width of the plates in addition to the vertical height of the wall.
Thus it is an additional preferred step in the process of forming the reinforcement of the wall that an array in the form of a table, containing calculated spacing distances, be consulted and that the plates be spaced according to the table.
Fabrication of the reinforcing plates of this invention comprises embedding a layer of carbon or glass or other reinforcing fibers in a matrix of resin that can be vinylester, polyester, epoxy or an other type. Next, the resin is cured resulting in a rigid plate having a predetermined structural strength. The fibers are oriented in parallel relationship and of a length to extend the full longitudinal length of the plate.
Mechanical anchoring of the plates to the wall at their top and bottom ends through use of fastening devices in combination with anchor plates is also contemplated to enhance the attachment strength of the plates to the wall. These anchor plates may be square sections of the reinforcing plate placed in overlying relationship to the outwardly facing surface of the plates and secured thereto by an adhesive bonding agent. Rectangular sections of the reinforcing plate may also be used, thereby distributing the anchoring force over an elongated length of a plate.
In a second embodiment of this invention the reinforced fibers are formed into a fabric-type sheet of material. The fibers are disposed in parallel, closely adjacent relationship forming a layer that is secured together by transversely extending high tensile strength fibers. This sheet is designed to be positioned in coplanar, overlying relationship to the interior surface of the masonry wall to which it is secured by a bonding resin, thereby providing waterproofing in addition to strengthening the wall.
Although the waterproofing sheet can be utilized by itself as described in the preceding paragraph it can also be used in combination with the rigid, fiber reinforced polymer plates. After application of the plates, the waterproofing sheet is applied. It may either be applied in a single, continuous sheet that overlies the vertically extending plates, or it may be applied in sections that fit between adjacently disposed pairs of the plates, and abut facing edges of each plate. The combination provides significant enhancement of the strengthening effect along with the added advantage of providing waterproofing.
An adhesive bonding resin is utilized in both securing a first sheet to the wall and in bonding the fibers in the sheet together as the resin will absorb into the mat as the resin is adsorbed by each fiber, and between the fibers when the sheet is pressed against the wall. Similarly, an adhesive bonding agent is applied to the outer surface of a previously applied sheet and bonds the next sheet to the prior sheet in addition to being absorbed by the fibers of this next applied sheet as it is pressed against the prior sheet.
In addition to forming in situ sheets, such as the waterproofing sheets described above, it is also contemplated that narrow strips of a similar fabric can be used to form reinforcing members mounted to the wall. These in situ formed reinforcing members are spaced, as described above, according to the necessary reinforcement of the wall.
Because a saturating adhesive can be absorbed too rapidly into the porous wall by capillary action, it is also an embodiment of the invention to apply a more highly viscous paste epoxy or other suitable filler to the wall prior to mounting the waterproofing sheet and the fabric strips to the wall. The paste adheres to the porous wall but prevents the lower viscosity saturating adhesive from being drawn from the fabric sheets or strips.
Additionally, it is contemplated to form, such as by sawing, a plurality of grooves in a wall and insert adhesive in the groove. Next, an elongated bar, such as a cylindrical rod, is placed in the groove. This forces the adhesive against the groove walls and permits substantial adhesion thereto. The adhesive is preferably smoothed to form a continuous surface on the interior wall surface.
Utilization of this invention is particularly advantageous with masonry or concrete walls but its utility is not limited to those walls. The strengthening and waterproofing elements may be used with the walls of structures fabricated from other materials such as, for example, wood or metal.
It is the primary objective of this invention, therefore, to provide an effective method of strengthening masonry or concrete walls of the type herein described after they have been constructed. This is accomplished by applying components at and near the interior surface of a wall thereby avoiding relatively costly work on the exterior of the wall.
These and other objects and advantages of this invention will become more clearly apparent from the following detailed description of the invention and the accompanying drawings.